1. Field of the Invention
This invention relates to a method of assembling a valve drive mechanism in an internal combustion engine and, more particularly, to a method of assembling a valve drive mechanism with a variable valve timing feature in an internal combustion engine.
2. Description of Related Art
Since the advanced development of internal combustion engines, it has been recognized that greater power output and efficiency can be achieved if intake and exhaust valve operations can be varied as a function of an engine operating condition such as engine speed. Engines typically have a timing belt provided between an engine crankshaft and either an intake or an exhaust camshaft, operationally coupled to each other by camshaft gears attached to the respective camshafts. In this manner, intake and exhaust valves are driven. One way to accomplish a variation in valve timing in such engines is to vary the phase of rotation of one camshaft relative to the other. Such a variable valve timing mechanism is known from, for instance, Japanese Unexamined Patent Publication No. 62-191636.
During assembly of the valve drive mechanism with a variable valve timing feature to an engine, because various rotational elements of the valve drive mechanism must be "well timed", i.e., operate at particular times relative to one another, installing the camshaft gear in the variable valve timing mechanism attached to one of the intake and exhaust camshafts typically is troublesome. In order for the intake and exhaust valves to open and close at proper times, the relative rotation phases of the intake and exhaust camshafts must be adjusted. For phase adjustment of the camshafts, it is necessary to adjust a predetermined relative angular position existing between the camshaft gears of the intake and exhaust camshafts and between the variable valve timing mechanism and both the camshaft and the camshaft gear which cooperate with the variable valve timing mechanism.
When making such an adjustment in relative angular position for phase adjustment by, for instance, a pin-and-slot type connection or engagement, if a lock means, such as a lock nut or a lock bolt, is used to fasten the camshaft gear to the variable valve timing mechanism or the variable valve timing mechanism to the camshaft, insufficient pin-and-slot engagement may occur. If insufficient pin-and-slot engagement does occur, the pin-and-slot engagement can break down completely. Accordingly, misadjustment of the relative phase of rotation between the intake and exhaust camshafts can be caused. Such misadjustment results in insufficient engine performance. Moreover, making a relative angular position adjustment two or more times decreases the efficiency with which assembling work is performed.